Practical Manual ofEchocardiography

Edited by Vladimir Fridmanand Mario J. Garcia

in the Urgent Setting

Practical Manual of Echocardiography in the Urgent Setting Edited by Fridman& Garcia

Practical Manual of Echocardiographyin the Urgent Setting

Mario J. Garcia MDProfessor, Department of Medicine (Cardiology); Professor, Department of Radiology; Chief, Division of Cardiology; Co-Director, Montefiore Einstein Center for Heart and Vascular Care. New York, NY, USA

Edited by:

Vladimir Fridman MDDepartment of CardiologyLong Island College HospitalNew York, NY, USA

In the acute care setting, medicine happens at full speed and with little margin for error. As echocardiography plays an ever more important role in the diagnosis of patients who present with symptoms that suggest a cardiovascular emergency, clinicians must learn to collect, process and act on echocardiographic information as quickly and effectively as possible.

Practical Manual of Echocardiography in the Urgent Setting covers the essentials of echocardiography in the acute setting, from ultrasound basics to descriptions of all pertinent echocardiographic views to clear, stepwise advice on basic calculations and normal/abnormal ranges.

This compact new reference:

$ Provides step-by-step guidance to acquiring the correct views and making the necessary calculations to accurately diagnose cardiac conditions commonly encountered in urgent settings.

$ Presents information organized by complaint/initial presentation so that readers can work from this first knowledge of the patient through the steps required to pinpoint a diagnosis.

$ Covers echo basics, from sound wave characteristics/properties to common device settings to basic ultrasound formulas.

$ Includes diagnostic algorithms fitted to address the differential diagnosis in the most commonly- encountered clinical scenarios.

Designed and written by frontline clinicians with extensive experience treating patients, Practical Manual of Echocardiography in the Urgent Setting is the perfect pocket-sized guide for residents in cardiology, emergency medicine, and hospital medicine; trainees in echocardiography; medical students on cardiology or emergency medicine rotations; technicians, nurses, attending physicians—anyone who practices in the urgent setting and who needs reliable guidance on echocardiographic views, data and normal/abnormal ranges to aid rapid diagnosis and decision-making at the point of care.

RELATED TITLES:

Kacharava, et al: Pocket Guide to Echocardiography; ISBN: 978-0-470-67444-4

Sun, et al: Practical Handbook of Echocardiography: 101 Case Studies; ISBN: 978-1-4051-9556-0

PG3628File Attachment9780470659977.jpg

Practical Manual of Echocardiography in the Urgent Setting

To:

– Dr Balendu Vasavada, whose knowledge and dedication to echocardi-ography has been the basis of this textbook. Many of the images in this book are a direct result of his leadership at the echocardiography laboratory of Long Island College Hospital.

– Dr Steven Bergmann, who served as a great mentor throughout my training and clinical practice. His tremendous assistance and dedication to cardiology have made my career possible.

– Dr Cesare Saponieri, who is responsible for all I know about the practice of clinical cardiology. His pursuit of providing great care to patients is truly an inspiration.

– Of course, Dr Mario Garcia for spending countless hours going through all the text, figures, and tables in this book. Without him, this book would not be possible.

– All of my cardiology colleagues who made this book a reality.

Thank you.

Practical Manual of Echocardiography in the Urgent Setting

EDITED By

Vladimir Fridman, mdCardiovascular DiseasesBrooklyn, Ny, USA

Mario J. Garcia, mdProfessor, Department of Medicine (Cardiology)Professor, Department of RadiologyChief, Division of CardiologyCo-Director, Montefiore Einstein Center for Heart and Vascular CareNew york, Ny, USA

A John Wiley & Sons, Ltd., Publication

This edition first published 2013, © 2013 by John Wiley & Sons, Ltd.

Wiley-Blackwell is an imprint of John Wiley & Sons, formed by the merger of Wiley’s global Scientific, Technical and Medical business with Blackwell Publishing.

Registered office John Wiley & Sons, Ltd, The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, UK.

Editorial offices 9600 Garsington Road, Oxford, OX4 2DQ, UKThe Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, UK111 River Street, Hoboken, NJ 07030-5774, USA.

For details of our global editorial offices, for customer services and for information about how to apply for permission to reuse the copyright material in this book please see our website at www.wiley.com/wiley-blackwell.

The right of the author to be identified as the author of this work has been asserted in accordance with the Copyright, Designs and Patents Act 1988.

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by the UK Copyright, Designs and Patents Act 1988, without the prior permission of the publisher.

Designations used by companies to distinguish their products are often claimed as trademarks. All brand names and product names used in this book are trade names, service marks, trademarks or registered trademarks of their respective owners. The publisher is not associated with any product or vendor mentioned in this book. This publication is designed to provide accurate and authoritative information in regard to the subject matter covered. It is sold on the understanding that the publisher is not engaged in rendering professional services. If professional advice or other expert assistance is required, the services of a competent professional should be sought.

The contents of this work are intended to further general scientific research, understanding, and discussion only and are not intended and should not be relied upon as recommending or promoting a specific method, diagnosis, or treatment by physicians for any particular patient. The publisher and the author make no representations or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties, including without limitation any implied warranties of fitness for a particular purpose. In view of ongoing research, equipment modifications, changes in governmental regulations, and the constant flow of information relating to the use of medicines, equipment, and devices, the reader is urged to review and evaluate the information provided in the package insert or instructions for each medicine, equipment, or device for, among other things, any changes in the instructions or indication of usage and for added warnings and precautions. Readers should consult with a specialist where appropriate. The fact that an organization or Website is referred to in this work as a citation and/or a potential source of further information does not mean that the author or the publisher endorses the information the organization or Website may provide or recommendations it may make. Further, readers should be aware that Internet Websites listed in this work may have changed or disappeared between when this work was written and when it is read. No warranty may be created or extended by any promotional statements for this work. Neither the publisher nor the author shall be liable for any damages arising herefrom.

ISBN: 9780470659977

A catalogue record for this book is available from the British Library.

Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books.

Cover Design: Modern Alchemy LLCCover image: Mike Austin

Set in 9/12 pt Palatino by SPi Publisher Services, Pondicherry, India

Printed and bound in Singapore by Ho Printing Singapore Pte ltd

1 2013

v

Contents

Contributors, xPreface, xiv

1 Ultrasound physics, 1Vladimir Fridman

Ultrasound generation, 7

Image formation, 9

Doppler ultrasound, 15

Summary and key points, 22

References, 22

2 The transthoracic examination, 23Vladimir Fridman and Dennis Finkielstein

Performing the echocardiogram, 33

Using the transducer, 35

Steps involved in a comprehensive transthoracic echocardiogram, 37

References, 40

3 Transesophageal echocardiography, 41Salim Baghdadi and Balendu C. Vasavada

Preparation of the patient, 42

Acoustic windows and standard views, 45

Clean-up and maintenance, 54

References, 56

vi | Contents

4 Ventricles, 57Deepika Misra and Dayana Eslava

Left ventricle, 57

Right ventricle, 66

Atria, 72

Contrast echocardiography, 74

References, 77

5 Left-sided heart valves, 79 Muhammad M. Chaudhry, Ravi Diwan, Yili Huang, and Furqan H. Tejani

Aortic valve, 79

Mitral valve, 94

References, 111

6 Right-sided heart valves, 113Michael J. Levine and Vladimir Fridman

Tricuspid valve, 113

Pulmonic valve, 122

Qp/Qs: Pulmonary to systemic flow ratio, 127

References, 127

7 Prosthetic heart valves, 129Karthik Gujja and Vladimir Fridman

Echocardiographic approach to prosthetic heart valves, 132

Approach to suspected valve dysfunction, 134

References, 140

8 The great vessels, 141Vladimir Fridman and Hejmadi Prabhu

Aorta, 141

Pulmonary artery, 147

D-septal shift, 151

References, 152

9 Evaluation of the pericardium, 153Chirag R. Barbhaiya

Pericardial effusions, 153

Cardiac tamponade, 154

Echo-guided pericardiocentesis, 159

Contents | vii

Constrictive pericarditis, 161

Differentiation of constrictive pericarditis and restrictive cardiomyopathy, 163

Effusive–constrictive pericarditis, 165

References, 165

10 Specialty echocardiographic examinations, 167Cesare Saponieri

TTE in a VAD patient, 167

Intracardiac echocardiography, 169

TEE in the operating room, 171

Echocardiography to guide percutaneous closure devices placement, 172

References, 173

11 Common artifacts, 174Padmakshi Singh, Moinakhtar Lala, and Sapan Talati

References, 182

12 Hypotension and shock, 183Sheila Gupta Nadiminti

Determination of central venous pressure, stroke volume, cardiac output, and vascular resistance, 183

Hypovolemia, 184

Septic shock, 188

Cardiogenic shock due to left ventricular failure, 189

Cardiogenic shock due to right ventricular failure, 189

Cardiogenic shock due to acute valvular insufficiency or shunt, 190

Acute pulmonary hypertension/pulmonary embolism, 190

References, 193

13 Chest pain syndrome, 195Sandeep Dhillon and Jagdeep Singh

Myocardial Infarction, 195

Aortic dissection, 198

Pulmonary embolus, 199

Other causes, 201

References, 202

viii | Contents

14 Cardiac causes of syncope and acute neurological events, 204Erika R. Gehrie

Hypovolemia, 205

Arrhythmias, 205

Aortic stenosis, 207

Cardiac tamponade, 207

Pacemaker malfunction, 207

Endocarditis, 207

Pulmonary embolism, 208

Stroke and transient ischemic attacks, 208

Cardiac masses, 212

References, 215

15 Acute dyspnea and heart failure, 216Mariusz W. Wysoczanski

Echocardiogram in “heart failure”, 216

Intracardiac pressures, 217

Echocardiographic approach to dyspnea with hypoxemia, 222

Differential diagnosis for cardiac induced dyspnea, 223

Algorithm for treatment, 223

References, 225

16 Evaluation of a new heart murmur, 226Vinay Manoranjan Pai

Acute valvular regurgitation, 226

Intracardiac shunts, 231

Pericardial effusion, 232

Post myocardial infarction, 232

References, 233

17 Infective endocarditis, 234Luis Aybar

Diagnosis and diagnostic accuracy, 234

Guidelines for use of echocardiography to diagnose endocarditis, 236

Appearance on echocardiography, 236

Complications and risk stratification, 238

Contents | ix

Prosthetic valve endocarditis, 239

Cardiac device-related infective endocarditis, 240

References, 241

18 Post-procedural complications, 244Vladimir Fridman

Noncardiac procedures, 244

Cardiac procedures, 245

References, 247

19 “Quick echo in the emergency department”: What the EM physician needs to know and do, 248Dimitry Bosoy and Alexander Tsukerman

Goal of FOCUS, 248

Clinical use of FOCUS, 250

References, 252

Index, 253

Contributors

Luis Aybar, MDCardiovascular DiseasesBeth Israel Medical CenterNew york, Ny, USA

Salim Baghdadi, MDDepartment of CardiologyLong Island College HospitalNew york, Ny, USA

Chirag R. Barbhaiya, MDCardiology FellowBeth Israel Medical CenterNew york, Ny, USA

Dimitry Bosoy, MDClinical Teaching AttendingDepartment of Emergency MedicineMaimonides Medical CenterBrooklyn, Ny, USA

Muhammad M. Chaudhry, MDCardiology FellowBeth Israel Medical CenterNew york, Ny, USA

Sandeep Dhillon, MD, FACCCardiovascular DiseasesBeth Israel Medical CenterNew york, Ny, USA

Ravi Diwan, MDBeth Israel Medical CenterNew york, Ny, USA

x

Contributors | xi

Dayana Eslava, MDSt Luke’s Roosevelt HospitalColumbia University College of Physicians and SurgeonsNew york, Ny, USA

Dennis Finkielstein, MD, FACC, FASEDirector, Ambulatory CardiologyProgram Director, Cardiovascular Diseases FellowshipBeth Israel Medical Center, New york, Ny, USAAssistant Professor of MedicineAlbert Einstein College of MedicineNew york, Ny, USA

Karthik Gujja, MD, MPHDivision of CardiologyDepartment of Internal MedicineLong Island College HospitalNew york, Ny, USA

Erika R. Gehrie, MD, FACCMedical Director, EchocardiographyPreferred Health Partners,Brooklyn, Ny, USA

Yili Huang, DO, FACCBeth Israel Medical CenterNew york, Ny, USA

Moinakhtar Lala, MDFellow in Cardiovascular DiseasesCardiovascular DiseasesBeth Israel Medical CenterNew york, Ny, USA

Michael J. Levine, MDCardiovascular DiseasesNyU Langone Medical CenterNew york, Ny, USA

Vinay Manoranjan Pai, MBBS, MDFellow, Cardiovascular MedicineBeth Israel Medical Center and Long Island College HospitalNew york, Ny, USA

xii | Contributors

Deepika Misra, MBBS, FACCBeth Israel Medical CenterNew york, Ny, USA

Sheila Gupta Nadiminti, MDDepartment of CardiologyBeth Israel Medical CenterNew york, Ny, USA

Hejmadi Prabhu, MDCardiovascular DiseasesWyckoff Heights Medical CenterBrooklyn, Ny, USA

Cesare Saponieri, MD, FACCElectrophysiology and Cardiovascular DiseasesBrooklyn, Ny, USA

Jagdeep Singh, MBBSCardiovascular DiseasesBeth Israel Medical CenterNew york, Ny, USA

Padmakshi Singh, MDFellow in Cardiovascular DiseasesCardiovascular DiseasesSUNy Downstate Medical CenterBrooklyn, Ny, USA

Sapan Talati, MDFellow in Cardiovascular DiseasesSUNy Downstate Medical CenterBrooklyn, Ny, USA

Furqan H. Tejani, MD, FACC, FSCCTAssociate Professor of MedicineDirector, Advanced Cardiovascular ImagingDirector, Nuclear Cardiology and Electrocardiography LaboratoriesState University of New yorkDownstate Medical CenterUniversity Hospital of Brooklyn at Long Island College HospitalBrooklyn, Ny, USA

Alexander Tsukerman, MD, FACEPAttending, Emergency MedicinePartner, Emergency Medical AssociatesStaten Island, New york, Ny, USA

Contributors | xiii

Balendu C. Vasavada, MD, FACCDirector of Echocardiography and Chief of Cardiology ServiceUniversity Hospital of Brooklyn at Long Island College HospitalSUNy Downstate Medical CenterNew york, Ny, USA

Mariusz W. Wysoczanski, MDFellow, Cardiovascular DiseasesBeth Israel Medical CenterAlbert Einstein College of MedicineNew york, Ny, USA

xiv

Preface

There will be times when you will need to read a comprehensive echocar-diography textbook. However, there will be also times when you will need to access quick reference information to help you manage a crashing patient in an urgent situation. This reference guide will provide you everything you need to establish a differential and accurate diagnosis that will lead you to best manage a cardiovascular patient in an emergent situation.

With the first part devoted to basic instrumentation and image acquisi-tion and the second part focusing on the different clinical situations that often require evaluation by echocardiography in the urgent setting, this book is the ideal companion to the physician who needs to implement rapid life and death decisions.

you should use this book as a quick reference guide to echocardio-graphy in the urgent setting. It is designed to help in situations where seconds and minutes can really make a difference in the lives of patients. Even one extra saved life will justify the large amount of work that the authors have put into this work.

Vladimir Fridman and Mario Garcia

Practical Manual of Echocardiography in the Urgent Setting, First Edition. Edited by Vladimir Fridman and Mario J. Garcia. © 2013 John Wiley & Sons, Ltd. Published 2013 by John Wiley & Sons, Ltd.

1

Ultrasound physicsVladimir FridmanCardiovascular Diseases, New york, Ny, USA

Echocardiography is one of the most valuable diagnostic tests for the evaluation of patients with suspected cardiovascular disease in the acute setting. Even though echocardiography has become more widely available, its performance and interpretation require practice and knowledge of the principles of image formation. Although the physical principles and instrumentation of ultrasound can be quiet complex, there are a few basic concepts that every echocardiographer and interpreting physician must understand to maximize the diagnostic utility of this test and avoid misinterpretations. These key concepts are covered in this chapter.

The echocardiogram machine (Figure 1.1) is made up of few distinct components:1 Monitor2 CPU (central processing unit), responsible for all functions of the

echocardiogram3 Transducer4 Keyboard/controls5 PrinterThe control panel of any echocardiogram looks similar to that shown in Figure 1.2a. The panel is shown in more detail in Figures 1.2b–d, with the important controls labeled. Although slight changes in control positions are noted between machines from different companies, all machines have the key controls that are shown in these images.

The panel from above image, is split into three frames, and the impor-tant controls are labeled below.

CHAPTER 1

2 | Chapter 1

Monitor

Keyboard

Printer

Transducer

CPU

Figure 1.1 Echocardiogram machine.

Figure 1.2 Typical echocardiogram control panel.

Keyboard

Trackball

On/off (a)

Ultrasound physics | 3

Dynamic range

Position

Depth

Gain

Time gain compensation

Record/clip store

Baseline/scale

(c)

M-mode

PW doppler

Transducer select

CW doppler

Begin/end study

Review films

(b)

Figure 1.2 (Cont’d)

4 | Chapter 1

The important echocardiographic settings as displayed on the monitor of most ultrasound machines are shown in Figure 1.3. These settings can be changed, as needed, to adjust the image quality.

The different echocardiographic modes that are available, which are described later in this book, are:

• M-mode: a graphic representation of a specific line of interest of a two-dimensional image (Figure 1.4).

Transducer frequency

Transducer type

Patient’s heart rate

Recording controls

Doppler settings

Mechanical index/dynamic range

Type of study

Time of study

Figure 1.3 Echocardiography settings.

Figure 1.2 (Cont’d)

Freeze/move forward/back

Mouse controls

Color doppler

(d)

Ultrasound physics | 5

• 2D: a two-dimensional view of cardiac structures that can be visual-ized as time progresses (Figure 1.5).

• Color Doppler: a color representation of blood flow velocities superimposed on a two-dimensional image (Figure 1.6).

• CW/PW Doppler: the representation of flow velocities as plotted with time on the x axis and velocity on the y axis (Figure 1.7).

• Tissue Doppler: the measurement of tissue velocities (Figure 1.8).The controls, as shown in the figures, switch between the different modes of echocardiography. However, before moving on to performing and

Figure 1.4 M-Mode: a graphic representation of a specific line of interest of a two-dimensional image.

Figure 1.5 2D: a two-dimensional view of cardiac structures that can be visualized as time progresses.

6 | Chapter 1

Figure 1.7 CW/PW Doppler: the representation of flow velocities as plotted with time on the x axis and velocity on the y axis.

Figure 1.6 Color Doppler: a color representation of blood flow velocities superimposed on a two-dimensional image.

Ultrasound physics | 7

interpreting echocardiograms, it is necessary to be aware of the physics behind this imaging modality.

Ultrasound generation

Ultrasound is a cyclic sound pressure waveform whose frequency is greater than the limit of human hearing. This number is generally consid-ered to be 20 kHz, or 20 000 Hz (Hertz). Echocardiography usually relies on sound waves ranging from 2 to 8 MHz. The echocardiograph, or any other medical ultrasound machine, produces these high frequency sound waves using transducers that contain a piezoelectric crystal.

A piezoelectric crystal (such as quartz or titanate cyramics) is a special material that compresses and expands as electricity is applied to it. This compression and expansion generates the ultrasound wave. The rate (frequency) of compression and expansion is based on the current that the ultrasound machine applies to the piezoelectric signal, which in turn is based on the settings the operator has selected on the machine.

An ultrasound wave, as all sound waves, has some basic physical properties (Figure 1.9). These are:

• Cycle – the sum of one compression and one expansion of a sound wave.

• Frequency (f) – the number of cycles per second. • Wavelength (λ) – the length of one complete cycle of sound. • Period (p) – the time duration of one cycle. • Amplitude – the maximum pressure change from baseline of a sound wave.

• Velocity (v) – speed at which sound moves through a specific medium.

Figure 1.8 Tissue Doppler: the measurement of tissue velocities.

8 | Chapter 1

A basic property of all sound waves is: Velocity = Frequency (f) x Wavelength (λ). This formula shows that frequency and wavelength are inversely related, since the velocity of a sound wave depends on the density of the medium the wave is traveling in.

In an echocardiogram machine, current is applied to the piezoelectric crystal, which then emits ultrasound energy into human tissue. The ultra-sound is emitted in pulses that usually consist of several consecutive cycles of a sound wave with the same frequency separated by a pause (Figure 1.10). An extremely important concept for ultrasound is the frequency of pulses that the ultrasound emits; this is called the Pulse Repetition Frequency (PRF). The inverse of PRF is the Pulse Repetition Period (PRP), which is the time from the beginning of one ultrasound pulse to the next:

=PRF 1/ PRP

Wavelength

Pulse length

Distance

High

Aco

ustic

var

iabl

e

Normal

Low

Listening time

Figure 1.10 A pulse can consist of multiple wavelengths of a sound wave. In this figure, three pulses are shown, each the length of two wavelengths (Reproduced from Case [2], with permisison from Elsevier).

Pre

ssur

eCompression

Rarefaction

λ

Time

Amplitude

Figure 1.9 A sound wave is made up of varying pressure cycles formed by repeating of compression and rarefaction. The distance between similar points in a wave is called the wavelength (λ) [1].

Ultrasound physics | 9

The actual length of the pulse – the spatial pulse length (SPL) – is equal to the wavelength multiplied by the number of cycles in a pulse.

Once an ultrasound pulse is emitted from the transducer, the entire mech-anism enters the “listening” phase. At this time, the ultrasound machine is waiting to receive back the pulse it emitted after it was reflected from dis-tant structures. It is important to know that the ultrasound machine spends almost 99% of the time listening for, and 1% of the time generating, a signal.

Image formation

As the ultrasound wave exits the echocardiogram probe, it enters the human tissue. When the ultrasound waves encounter a change in tissue density, such as the endocardium–blood interphase, some of them will be reflected back while others will penetrate deeper into the tissue. Thus, ultrasound energy is greater near the transducer and is progressively lost as it penetrates into the tissue. The ultrasound systems typically compen-sate by amplifying more the signals that are received from the far field to make the image homogeneous. The interaction of ultrasound with human tissue is also very complex. However, it is important to know that within soft tissue the velocity of ultrasound is fairly constant at 1540 m/s. In fact, it is usually assumed that this is the velocity of sound in human tissue. However, it is not always the truth. The velocities of ultrasound in var-ious human tissues are shown in Table 1.1.

This concept is extremely important, since the ultrasound machine is not able to recognize whether the ultrasound it receives back from the body traveled mainly through bone, through soft tissue, through air, or any combination of the above structures. As such, it computes the dis-tance the ultrasound traveled based on a velocity of 1540 m/s. Therefore, objects can be misplaced on an ultrasound image because of this velocity assumption, which is built into the ultrasound machine. This explains

Table 1.1 Velocity of ultrasound in various human tissues.

Medium Velocity (m/s)

Air (the slowest) 330

Soft tissue 1540

Blood 1570

Muscle 1580

Bone (the fastest) 4080

10 | Chapter 1

why interposition of ribs or lung tissue between the transducer and the heart will produce severe imaging artifacts and make part of the image uninterpretable (Figure 1.11).

Another important point to remember is the behavior of the ultrasound beam as it emerges from the transducer (Figure 1.12). The ultrasound beam is initially parallel and cylindrical (near zone). However, after its narrowest point, the focal zone, it begins to diverge and acquires a cone shape (far zone). For reasons outside the scope of this book, the imaging is much better if the object of interest is located near the focal zone. The near zone length is calculated via: near field = (radius of transducer)2/wavelength of ultra-sound. The location of the focal zone can be adjusted electronically.

Figure 1.11 An apical four-chamber view of the same patient when the patient has exhaled (a), as the patient is inhaling (b), and as the patient is fully inhaled (c). As clearly seen, the quality of the myocardial image declines acutely as more air enters the lung of the patient, to a point where no myocardium is seen in full inhalation (c).

(a) (b)

(c)

Ultrasound physics | 11

Resolution versus penetrationThe behavior of the beam within tissue determines the lateral resolution of the ultrasound, or the ability to distinguish two objects located side by side on an ultrasound image. The axial resolution, or the ability to distin-guish two objects one in front of the other, on an ultrasound image is determined by ultrasound transducer frequency (1/wavelength). At higher frequency, axial resolution increases. However, since the ultrasound signal is attenuated as it travels through the tissues, more attenuation occurs. In general, high frequency is preferred for imaging structures that are closer to the transducer and lower frequency for those that are far. In the case shown in Figure 1.13, a parasternal long axis view loses its definition as the transducer frequency is changed from 4.0 MHz to 2.0 MHz.

As the ultrasound comes back to the transducer, the same piezoelectric properties of crystal that allow the ultrasound waves to be made allow the conversion of the received ultrasound waves into electrical signals. A  typical 2D ultrasound transducer has 128 or 256 individual crystal-electronic interphases. In M-mode imaging, the ultrasound beam is emitted and received only at 90°. By alternating the time and sequence in

Nearfield

Focalzone

Farfield

Figure 1.12 Behavior of an ultrasound beam as it comes out of the ultrasound probe (Reproduced from [2] Case, TD. Ultrasound Physics and Instrumentation. Surg Clinc N Am. 1998;78(2):197–217).

Figure 1.13 Image changes with a decrease in ultrasound frequency.

12 | Chapter 1

which these are stimulated, the ultrasound beam can be steered at almost any angle. By steering rapidly while emitting and receiving at sequential angles a two-dimensional image is formed (Figure 1.14).

Figure 1.14 As the scan line density increases (a→b), the accuracy and resolution of the image increase. As the sector angle (θ) increases (c→d), more structures are noted as the area being interrogated by the ultrasound beam increases. However, going to a narrower angle (e→f) increases resolution, as is seen in this set of images where a wider view (e) shows multiple structures, while the same view with a narrower sector angle (f) more clearly shows the endocardial definition of the left ventricle.

(a) (b)

θ

(c)

θ

(d)

(e) (f)